In a typical process for fabricating a semiconductor integrated circuit, various processes, such as deposition, oxidation/diffusion and etching, on the surface of a semiconductor wafer serving as an object to be processed are repeatedly carried out.
During the process for fabricating the semiconductor integrated circuit, the formation of wiring films and the filling of irregularities, such as contact holes and through holes, tend to use a metal tungsten film which is difficult to be broken even if being scaled down, easy to be attached, and has a low specific resistance.
As a method for depositing such a metal tungsten film, there is generally known a method for using, e.g., a tungsten hexafluoride (WF6) gas, as a tungsten metal containing raw material gas, to reduce it with H2 gas, as a reducing gas, to deposit a tungsten film. In this case, the deposition temperature is generally set to be 440° C. on the surface of the wafer. The reasons for this are that, if deposition temperature is low, stress in the film increases to warp the semiconductor wafer itself and/or to peel away the film, and deposition rate decreases to extremely decrease throughput. In general, the temperature of a supporting table (susceptor) is higher than the temperature of the wafer by about 20° C.
In recent years, the allowable quantity of thermal diffusion and so forth decreases due to a tendency for a semiconductor integrated circuit to be further scaled down and multilayered, it is required to avoid exposing a semiconductor wafer to high temperatures during the fabrication of a circuit, so that it is desired that the deposition temperature of a tungsten film on the surface of the wafer is lower than 440° C., e.g. 420° C. or lower.
In the circumstances, as described in, e.g., Japanese Patent Laid-Open No. 4-74865, there is proposed a method for using B2H2 (diborane), SiH4 (mono-silane), PH3 (phosphine) or the like as a reducing gas in place of H2, so as to deposit a tungsten film having good characteristics to some extent even in a low temperature region of about 300° C.
However, in the method disclosed in, e.g., Japanese Patent Laid-Open No. 4-74865, although it is certainly possible to deposit a metal tungsten film in a low temperature region, there are problems in that stress in the film is very large and the deposition rate remains to be not so high.